Mail sorting machines provide postal patrons that handle high volumes of mail with the ability to take advantage of the United States Postal Service's reduced postal rates. The United States Postal Service defines its postal class structure in a manner that generally provides lower rates based upon certain criteria such as the length (five digits versus nine digits) and manner (bar-coded or not) by which the zip code information is provided, and also the number of mail pieces that are included in a given package (a certain number of mail pieces, such as ten or more). Thus, a postal patron can achieve a considerable postage savings for bulk mailing by qualifying for less expensive pre-sorted and bar-coded rates. Sorting machines may also be used to sort incoming mail that has already been processed by the United States Postal Service.
Such automated mail sorting machines include Bell & Howell Company models J1000, J800 and J600 Mail Processing Systems and are provided by the Phillipsburg Division of Bell & Howell Company. These automated sorting machines write or optically read characters, and/or bar code labels and sort mail into various bins based upon detected ZIP code information.
Typically a mail sorting machine receives multiple mail pieces in an input hopper whereafter the mail pieces are transported to an extraction device which orientates each mail piece and feeds it to the transport path. Such a system is described in U.S. Patent Application of Paul F. Kostyniuk, assigned to instant assignee, entitled "Mail Sorting Apparatus and Method," filed Oct. 16, 1990, and is hereby incorporated by reference. The transport path generally provides for single file flow of the documents past the various stations of the sorting machine. Once a mail piece enters the transport path, a character reader reads the address and/or ZIP code written on the mail piece. A computer determines whether the ZIP code is a valid ZIP code and communicates the ZIP code digits to a bar code label printer. The label printer prints the bar-code label at the proper location on the mail piece. As the mail piece proceeds along the transport path, a bar code reader verifies whether a legitimate ZIP code label is printed and whether that ZIP code is attached to the proper mail piece.
In mail sorting systems such as these, accurate surveillance and alignment of documents is critical. Various problems arise along the transport path when an inadequate document tracking system is in place. These problems, which are aggravated as the speed of the system is increased, include document jamming, delayed document separation, and document "disappearance."
Document jamming occurs when a document gets caught along the transport path. One type of document jamming is called document shingling. Document shingling occurs when two or more documents appear to be a single document to the system such as when two documents are too close together or are stuck together. Delayed document separation occurs when two documents that have been fed together, separate later along the transport path. Document "disappearance" occurs when a document exits the sorting system prematurely or gets "trapped" in a section of the transport path where it cannot be detected.
Current sorting systems label mail pieces based upon a mail piece's assumed position in a queue. This type of sorting system detects when a first document enters the transport path and assumes that the first document to enter is the first document to leave the transport path. Such a system typically mislabels and missorts documents when a document inadvertently leaves the transport path. An example of this occurs when a document has been detected as properly entering the transport path and has its ZIP code properly read by the optical character reader. When this document is extracted by an operator or otherwise removed from (e.g., flies off or drops off of the transport path) the transport path before reaching the bar code printer, the system automatically marks the next document with the ZIP code information designated for the missing document assuming that the next document in line was the proper document. No real time automatic document surveillance system exists to prevent this type of error.
Known systems also fail not only to detect many of these problems, but they also fail to adequately correct many of these problems. For example, current systems that are able to detect a shingling event, flush the entire sorting system instead of minimizing its effects. This results in additional resorting of properly sorted documents. The shingling event is typically detected by shingling sensors at the beginning and end of the transport path.
Other systems fail to differentiate one type of error from another. An example is a document "disappearance" event wherein the system considers this event as a shingling event. System errors are not properly identified thereby limiting the ability to provide corrective measures. Thus, it is desirable to properly detect and correct disappearance errors and other errors without requiring a flushing of the transport path or other area of the sorting system.
There exists a need for a high speed intelligent automatic document sorting system that effectuates accurate (real time) document surveillance and provides error correction techniques to overcome the above mentioned problems. Such a system preferably should not require flushing the entire sorting system for all detected errors, but should correct errors to improve document throughput. The system should also accommodate fast transport path speeds without substantially increasing undetected sorting errors.